The production of nitrite and nitrous oxide (N2O) in the environment is directly related to the problems of public health. Nitrite is a precursor of nitrosamines, many of which are known as potent mutagenic and carcinogenic compounds. N2O is a natural quencher of stratospheric ozone. Since the input of combined nitrogen to the environment has been increasing rapidly because of the higher demand for increased food production, the flux and concentration of inorganic nitrogen compounds produced during the nitrogen cycle may be increasing as a result of the higher inputs of combined nitrogen. Because increased production of nitrite may increase the concentration of nitrosamines in the environment, and because increased production of N2O will increase the incidence of skin cancer, it is important to undersand factors that control the production of these nitrogen compounds. To examine factors influencing nitrite and N2O formation by two environmentally significant bacteria, nitrifiers and methane oxidizing bacteria, experiments will be initiated with batch cultures. Variables to be investigated include the influence of concentration of energy source, partial pressure of oxygen, pH, and temperature on the formation of nitrite and N2O by these organisms. Variables will be tested singly and in combination to determine their influence on the production of nitrite and N2O formation in continuous cultures which can be operated to simulate conditions of natural environments. Some experiments will be carried out with mixed cultures of nitrifiers and methanotrophs along the lines described above. These will provide information of relative significance of these two types of organisms for nitrite and N2O production in the environment.